National Instruments TBX-1329 User manual

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™, and SCXI™are trademarks of National Instruments Corporation. Product and company names mentioned herein are
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371215A-01 ©Copyright 1997, 2000 National Instruments Corp.All rights reserved. December 2000
INSTALLATION GUIDE
TBX-1329 AC/DC COUPLING TERMINAL BLOCK
This guide describes how to install and use the TBX-1329 AC/DC coupling
terminal block with the SCXI-1120, SCXI-1120D, SCXI-1121,
SCXI-1125, and SCXI-1126 modules.
Introduction
The TBX-1329 is a shielded, DIN-rail mountable terminal block with
screw terminals to connect to the SCXI-1120, SCXI-1120D, SCXI-1121,
SCXI-1125, or SCXI-1126 front connector. The TBX-1329 mounts on
most European standard DIN EN mounting rails.
The terminal block has 16 screw terminals for easy connection. Two screws
are provided to connect to the SCXI functional earth terminal through the
SH32-32-A cable shield. With the SCXI-1120, SCXI-1120D, SCXI-1125,
or SCXI-1126, the remaining eight pairs of screw terminals connect signals
to the eight SCXI module input channels. With the SCXI-1121, four pairs
of screw terminals connect signals to the four SCXI module input channels
and four pairs connect to the SCXI module excitation channels.
What You Need to Get Started
To set up and use your TBX-1329, you need the following:
❑TBX-1329 AC/DC coupling terminal block
❑TBX-1329 AC/DC Coupling Terminal Block Installation Guide
❑1/8 in. flathead screwdriver (included in kit)
❑SCXI chassis and documentation

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❑One of the following modules and its documentation:
– SCXI-1120
– SCXI-1120D
– SCXI-1121
– SCXI-1125
– SCXI-1126
❑SH32-32-A shielded cable assembly that includes the TBX cable
adapter
❑Long-nose pliers
❑3/16 in. wrench
❑Number 1 Phillips-head screwdriver
Conventions
The following conventions are used in this guide:
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text that is a placeholder for a word
or value that you must supply.
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames and extensions, and code excerpts.
Safety Information
Caution Do not operate the device in an explosive atmosphere or where there may be
flammable gases or fumes.
Keep away from live circuits. Do not remove equipment covers or shields unless you are
trained to do so. If signal wires are connected to the device, hazardous voltages can exist
even when the equipment is turned off. To avoid a shock hazard, do not perform procedures
involving cover or shield removal unless you are qualified to do so and disconnect all field

©National Instruments Corporation 3 TBX-1329 Installation Guide
power prior to removing covers or shields.
Equipment described in this document must be used in an Installation Category II1
environment per IEC 60664-1. This category requires local level supply mains-connected
installation.
Do not operate damaged equipment. The safety protection features built into this device
can become impaired if the device becomes damaged in any way. If the device is damaged,
turn the device off and do not use it until service-trained personnel can check its safety.
If necessary, return the device to National Instruments for service and repair to ensure that
its safety is not compromised.
Do not operate this equipment in a manner that contradicts the information specified in this
document. Misuse of this equipment could result in a shock hazard.
Do not substitute parts or modify equipment. Because of the danger of introducing
additional hazards, do not install unauthorized parts or modify the device. Return the
device to National Instruments for service and repair to ensure that its safety features are
not compromised.
Yo u must insulate all of your signal connections to the highest voltage with which the
SCXI-1329 can come in contact.
When using the device with high common-mode voltages, you must insulate your signal
wires for the highest input voltage. National Instruments is not liable for any damages or
injuries resulting from inadequate signal wire insulation. Use only 26-14 AWG wire with
a minimum voltage rating of 300 V and a temperature value of 60 °C for measuring up
to 300 V.
When connecting or disconnecting signal lines to the SCXI terminal block screw terminals,
make sure the lines are powered off. Potential differences between the lines and the SCXI
ground can create a shock hazard while you connect the lines.
Connections, including power signals to ground and vice versa, that exceed any of the
maximum signal ratings on the SCXI device can create a shock or fire hazard, or can
damage any or all of the boards connected to the SCXI chassis, the host computer, and the
SCXI device. National Instruments is not liable for any damages or injuries resulting from
incorrect signal connections.
If hazardous voltages (≥30 Vrms and42.4V
peak or 60 VDC) are present, you must connect
a safety earth-ground wire to the terminal block safety-ground lug, shown in Figure 2. This
complies with safety agency requirements and protects against electric shock when the
terminal block is not connected to the chassis. To connect the safety earth-ground to the
safety-ground lug, run an earth-ground wire from the signal source to the terminal block.
1Category II refers to local-level power distribution, such as that provided by a standard wall outlet.

TBX-1329 Installation Guide 4 ni.com
National Instruments is not liable for any damages or injuries resulting from inadequate
safety earth-ground connections.
Do not loosen or re-orient the safety-ground lug hardware when connecting the
safety-ground wire; to do so reduces the safety isolation between the high voltage and
safety ground.
Clean the module and accessories by brushing off light dust with a soft non-metallic brush.
Remove other contaminants with a stiff non-metallic brush. The unit must be completely
dry and free from contaminants before returning it to service.
The terminal block must be used with a UL-listed SCXI chassis.
Strain-Gauge Voltage Drops When Using the SCXI-1121
When you use the SCXI-1121 with the TBX-1329 to measure strain,
a small amount of voltage drop develops across the excitation wires in
the SH32-32-A cable. This voltage drop is due to the wire resistance and
the current flow in these leads when a strain gauge is connected at the
TBX-1329 across the excitation outputs provided on the SCXI-1121.
To reduce errors in your output voltage, first you need to calculate the
voltage drop across the SH32-32-A cable. This voltage drop, which results
in an error in your measurement, depends on the cable length and on the
strain gauge value and configuration. The SH32-32-A cable has a
resistance of 0.21 Ω/m.
To determine the amount of error introduced by the cable, do the following:
1. Calculate the total resistance (RTL) of the cable based on the cable
length.
2. Refer to your strain-gauge data sheet for the bridge resistance of the
strain gauge (RSG) connected at the TBX-1329.
3. Use the following formula to determine the total voltage drop (Vdrop)
in the SH32-32-A cable excitation leads:
Vdrop =[RTL/(RTL +RSG)] x Vex
where Vex = excitation voltage.
For example, if you have a 1 m SH32-32-A cable, 120 Ωfull-bridge strain
gauge, and Vex = 3.333 V, your calculations from Steps 1 through 3 would
be:
1. RTL =2x0.21Ω/mx1m=0.42Ω; you multiply the cable length by
two to take into consideration both the Vex+ and Vex- lead resistances.
2. RSG =120Ω, is the total equivalent bridge resistance as seen from the
Vex ±terminals of the TBX-1329.

©National Instruments Corporation 5 TBX-1329 Installation Guide
3. Vdrop =11.6mV⇔0.3% of 3.333 V excitation.
You then need to calculate the voltage drop across the field signal wires you
are connecting to the TBX-1329. Perform similar calculations for your field
wires as you did for your cable. Resistance can vary depending on your
cable and field wires. Add this error amount to the voltage drop across the
SH32-32-A cable to get a total voltage drop.
You can compensate for this error along with any additional cable lead
resistance introduced by the strain-gauge connection wires. One simple
way of compensating is to calculate the lead resistance as shown in Steps 1
through 3, then input it along with your other strain-gauge parameters into
the conversion formula in your National Instruments data acquisition
software packages. In order to minimize resistive compensation, locate the
load closer to your SCXI module by using shorter cable lengths, or use
heavy-gauge wire to connect to the TBX-1329.
Measuring Current
To measure current with the TBX-1329, you can place a current loop
receiver resistor in the sockets on the TBX-1329. Table 1 shows the
TBX-1329 socket assignment per channel.
Caution Use only National Instruments SCXI process current resistor kits for current
measurements.
Table 1. Socket Assignments per Channel
Channel Number Resistor Designator
0R0
1R1
2R2
3R3
4R4
5R5
6R6
7R7

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Configuring AC/DC Coupling
Each channel of the TBX-1329 has two switches you can use to switch
from AC to DC; thus, you can configure each channel individually.
The factory-default setting for the switches is the DC position so that the
terminal block passes all signals, DC and AC, to the SCXI module. In the
AC position, the switches switch in a capacitor and, depending on which
module you use, a referencing resistor. This blocks the DC components
of the input signal and provides a true AC signal to the SCXI module.
Each switch is uniquely marked to make switch identification easier.
Each switch that switches the capacitor into the circuit is labeled with SCX.
Each switch that switches the resistor into the circuit is labeled with SRX.
The Xsymbol represents the channel number; for example, SC2 is the
capacitor switch for channel 2 and SR2 is the resistor switch for channel 2.
Table 2 shows the TBX-1329 terminal block switch settings.
Table 2. TBX-1329 Terminal Block Switch Settings
Switch Settings for
Each Channel Description
Switch Configuration
SCXI-1120,
SCXI-1121,
SCXI-1125, and
SCXI-1126 SCXI-1120D
DC coupling selected; removes
capacitor and resistor from the
circuit. Signals go straight
through.
Switch both SCX
and SRX switches
for DC coupling.
Switch both SCX
and SRX switches
for DC coupling.
AC coupling selected; SCX
connects the capacitor to the
circuit. SRX connects the resistor
to the circuit.
Switch both SCX
and SRX switches
for AC coupling.
Switch ONLY
SCX switch for
AC coupling. SRX
must be in the DC
position.
DC
AC
SCX
SRX
DC
AC
SCX
SRX

©National Instruments Corporation 7 TBX-1329 Installation Guide
Connecting the Signals
Note Refer to Safety Information before removing equipment covers or connecting or
disconnecting any signal wires.
When connecting your signals to the TBX-1329, follow the labeling on the
TBX-1329 for the appropriate module, as indicated in Figure 1. When
using the TBX-1329 with the SCXI-1125 or SCXI-1126, follow the
SCXI-1120/1120D labeling.
Figure 1. TBX-1329 Parts Locator Diagram
To connect the signal to the terminal block, perform the following steps
while referring to Figure 2:
1. Remove the TBX-1329 terminal block cover by unscrewing the four
captive cover screws in the cover corners. These screws stay attached
to the cover without falling out.
1 Current Loop Receiver Resistor
2 Safety Ground Solder Lugs
3 Product Name
4 Assembly Number
5 Serial Number
6 SR7/SC7
7 SR6/SC6
8 SR5/SC5
9 SR4/SC4
10 SR3/SC3
11 SR2/SC2
12 SR1/SC1
13 SR0/SC0
14 SCXI Module-Type Rows
12 11 10 9 8 613
1
2
14
2
1
345
300V MAX CHANNEL TO CHANNEL
300V MAX CHANNEL TO EARTH
7

TBX-1329 Installation Guide 8 ni.com
2. Prepare your signal wire by stripping the insulation no more
than 7 mm.
3. Connect the signal wires to the screw terminals by inserting the
stripped end of the wire fully into the terminals.
4. Tighten the terminals to a torque of 5-7 in.-lb (56-79 Newton cm).
5. Relieve strain on your signal wires by tie-wrapping them to the
mounting rails of your rack.
6. Replace the TBX-1329 terminal block cover and tighten the captive
cover screws.
Figure 2. TBX-1329 Parts Locator Diagram
1 Safety Ground Lugs 2 Captive Cover Screws 3 Terminal Block Connector 4 Signal Wire Entry
2
1
4
3
2

©National Instruments Corporation 9 TBX-1329 Installation Guide
Refer to your SCXI module user manual for examples of how to connect to
field signals and loads. The functional earth terminals are connected to the
SCXI chassis through the cable shield. This is not shown in your SCXI
module user manual. Allow your signal wires to exit through the TBX-1329
cover opening.
The signal connection is now complete.
Installing the Cable and Terminal Block
Perform the following steps to mount the SH32-32-A cable assembly and
connect the TBX-1329 to your SCXI module. Refer to Figures 3 through 5
as needed.
1. Turn off your SCXI chassis.
2. Turn off the computer that contains your data acquisition (DAQ)
device or disconnect the device from your SCXI chassis.
3. Connect the TBX cable adapter to the appropriate SCXI module and
secure it by tightening both thumb screws.
4. Verify that the four backshell mounting ears on the cable assembly are
in the position shown in Figure 3 and Figure 4. If not, remove the
backshell mounting ears and install them in the position shown.

TBX-1329 Installation Guide 10 ni.com
Figure 3. Connecting the SH32-32-A Cable to the SCXI Module
1 Backshell Mounting Screws and
Ears
2 Cable Assembly
3 Thumb Screws
4 SCXI Chassis
5 TBX Cable Adapter
3
2
4
3
5
1